A nuclear reactor has a core defining many parallel passages. Within the core are a plurality of fuel core assemblies containing fuel elements of radioactive material and a plurality of control elements supported in interrelated matrixes. The fuel elements create heat. The presence of the control elements relative to the fuel elements determines the reactivity of the fuel, and thus the output of the reactor. Coolant is forced through the passages over the fuel core assemblies and control elements for transferring the generated heat to a heat exchange mechanism, whereby steam can be produced externally of the reactor and used to perform useful work.
One form of nuclear reactor, known as the liquid metal fast breeder reactor uses molten sodium as the coolant. A pool type liquid metal nuclear reactor has a pool of molten coolant (typically sodium), a core submerged in the pool and pump and piping for circulating the coolant from a "cold pool" upwardly through the core to an overlying "hot pool" area and then through a heat exchanger and back to the cold pool at a reduced temperature. An intermediate fluid line through the heat exchanger picks up the heat for transfer to heat conversion means outside of the reactor.
Some reactors provide for a separate fuel storage vessel of coolant outside of the reactor and a storage basket for spent core assemblies in this vessel. Storage is necessary for spent fuel to allow fission decay cool down. New core assemblies are also positioned in the storage basket prior to use to allow temperature equalization.
In some reactors the storage basket is located in the reactor vessel, which eliminates the need for a separate storage vessel. Again, replacement of the core assemblies is periodically required. Accordingly, internal fuel handling equipment, including a lifting mechanism, are provided within the reactor vessel. The assembly handling equipment generally includes an exit ramp which allows for the mechanical movement of the core assemblies to and from the reactor vessel.
When the storage basket is contained in the reactor vessel, it normally is placed in the redan or hot pool area for it to be accessible to the assembly handling machine. This is not preferred, as the storage basket and assembly handling equipment are subjected to higher temperature and thermal transients. In the present system the storage basket and handling system are located in the cold pool, in order to reduce the temperature of the core assemblies during cool down. In addition, cooler temperatures reduce wear on the assembly handling equipment. However, a means of opening and closing the redan or "hot pool" container is required for such a system.
Prior art patent showing various methods of refueling nuclear reactors may be found in the following U.S. Patents; U.S. Pat. Nos.; 4,366,113, Gigou; 3,935,062, Keller et al.; 3,635,792, Barker; 4,450,134, Soot et al.; 3,600,277, Germer; and 3,271,262, Hutchinson et al.